The present invention relates generally to directing metal strip or sheet from a coil of the strip to and collecting metal strip from a rolling mill as a coil of the strip. More particularly, the invention relates to offsetting the effects of cyclic disturbances originating in a coil of metal being directed to or received from a rolling mill.
In most operations in which metal is rolled in a rolling mill, the uniformity of the thickness of the metal exiting the mill is adversely affected by cyclic disturbances of rotating coils of metal being unwound and directed to the mill, and rewound into a coil, as the metal is collected from the mill. The cyclic disturbances of the coils have frequencies that coincide with the fundamental frequency and harmonics thereof of the coil rotation.
The cause of the problem is fourfold, i.e., cyclic disturbances are caused by (1) dimensional abnormalities (ovalness and eccentricity) of the coils, (2) a resonance condition resulting from a mass/spring system exhibited by the coil being connected to the mill via the strip of material being unwound or rewound, which material is under tension, (3) mechanical friction or binding of the unwind or rewind drive systems, and (4) changes in the thickness of the strip caused by a previous rolling operation that experiences one or more of the above three conditions.